Precipitated silica

ABSTRACT

Silicas in the form of powder and substantially spherical beads or granules are characterized by a CTAB specific surface of 140 and 240 m 2 /g a high ultrasonic disaggregation factor, an average diameter, which is small after ultrasonic disaggregation, and optionally, a porous distribution, the porous volume formed by the pores with a diameter of 175 to 275 Å being less than 50% of the porous volume formed by the pores with diameters of 400 Å or less. The silicas may be used as reinforcing fillers for elastomers. The invention also concerns a method for preparing precipitated silica of the type comprising the reaction of an alkaline metal silicate M with an acidifying agent, resulting in a suspension of precipitated silica, and the separation and drying of said suspension, wherein precipitation is performed as follows: (i) an initial seed is formed comprising a portion of the total quantity of alkaline metal silicate M in the reaction, the silicate concentration (expressed as SiO 2 ) in said seed being less than 20 g/l; (ii) an acidifying agent is added to the initial seed until at least 5% of the quantity of M 2 O in the initial seed is neutralized; (iii) the acidifying agent and the remaining quantity of alkaline metal silicate M are added simultaneously so that the ratio of the quantity of added silicate (expressed as SiO 2 ) to the quantity of silica in the initial seed (expressed as SiO 2 ) is greater than 4 and at most 100.

This application is a continuation of application Ser. No. 08/446,797,filed Aug. 21, 1995, now abandoned.

The present invention concerns a novel process for the preparation ofprecipitated silica, in particular precipitated in the form of a powder,substantially spherical spherules, or granules, and their application asa reinforcing filler for elastomers.

FIELD OF THE INVENTION

Precipitated silica has long been used as a white reinforcing filler forelastomers, in particular for tires.

However, like all reinforcing fillers, it must capable of readymanipulation in, and above all incorporation into the mixtures.

BACKGROUND OF THE INVENTION

It is generally known that, in order to produce optimal reinforcingproperties from a filler, the latter must be present in the elastomermatrix in a final form which is both as finely divided as possible anddistributed as homogeneously as possible. These conditions can only besatisfied if the filler can be extremely easily incorporated into thematrix during mixing with the elastomer (filler incorporability) and candisaggregate or deagglomerate to a very fine powder (fillerdisaggregation), and if the powder produced by the disaggregationprocess described can itself disperse perfectly and homogeneously in theelastomer (powder dispersion).

Further, the silica particles have an annoying tendency to agglomerateamong themselves in the elastomer matrix because of mutual attraction.These silica/silica interactions limit the reinforcing properties to alevel which is far lower than that which could theoretically be achievedif all the silica/elastomer interactions which could be formed duringthe mixing operation were formed (this theoretical number ofsilica/elastomer interactions is known to be directly proportional tothe external surface area of the silica used).

These silica/silica interactions also tend to increase the rigidity andconsistency of the mixtures in the uncured state, making their use moredifficult.

It is difficult to find fillers which, while having a relatively largesize, readily disperse in elastomers.

SUMMARY OF THE INVENTION

The present invention aims to overcome the drawbacks described above andresolve the difficulty mentioned above.

More precisely, it provides a novel process for the preparation ofprecipitated silica which advantageously has improved dispersion (anddeagglomeration) abilities and/or reinforcing properties, in particularwhen used as a filler for elastomers, to provide the latter with anexcellent compromise between their different mechanical properties.

The invention also concerns precipitated silicas, preferably in the formof a powder, substantially spherical spherules or, optionally, granulesand which, while relatively large in size, have highly satisfactorydispersion (and deagglomeration) abilities. They also have improvedreinforcing properties.

Finally, the invention concerns the use of said precipitated silicas asreinforcing fillers for elastomers.

One of the objects of the invention is thus to provide a process for thepreparation of a precipitated silica comprising reacting an alkali metalM silicate with an acidifying agent to produce a suspension of aprecipitated silica, then separating and drying said suspension,characterised in that precipitation is carried out as follows:

(i) forming an initial seed comprising a portion of the total amount ofthe alkali metal M silicate used i the reaction, the concentration ofsilicate expressed as SiO₂ in said seed being less than 20 g/l,

(ii) adding acidifying agent to said initial seed until at least 5% ofthe quantity of M₂O present in said initial seed is neutralised,

(iii) simultaneously adding acidifying agent and the remaining quantityof alkali metal M silicate to the reaction medium such that the ratio ofthe quantity of silicate added (expressed as SiO₂)/quantity of silicatepresent in the initial seed (expressed as SiO₂), the consolidationratio, is greater than 4 and at most 100.

It has thus been discovered that a very low concentration of silicateexpressed in SiO₂ in the initial seed and an appropriate consolidationratio during the simultaneous addition step constitute importantconditions for ensuring that the products obtained have excellentproperties.

It should be noted that, in general, the process concerned is a processfor the synthesis of precipitated silica, ie., an acidifying agent isreacted with an alkali metal M silicate.

The choice of acidifying agent and silicate is made in known fashion.The acidifying agent is usually a strong mineral acid such as sulphuricacid, nitric acid or hydrochloric acid, or an organic acid such asacetic acid, formic acid or a carboxylic acid.

The silicate can be in any known form such as a metasilicate, disilicateor, advantageously, an alkali metal M silicate where M is sodium orpotassium.

In general, the acidifying agent used is sulphuric acid, and thesilicate used is sodium silicate.

When using sodium silicate, this generally has a SiO₂/Na₂O molar ratioof between 2 and 4, more particularly between 3.0 and 3.7.

Specifically, precipitation is carried out using the following steps ofthe process of the invention.

Firstly, a seed containing silicate is formed. The quantity of silicapresent in the initial seed advantageously only represents a portion ofthe total quantity of silicate used in the reaction.

According to an essential feature of the preparation process of theinvention, the concentration of silicate in the initial seed is leastthan 20 g of SiO₂ per liter.

This concentration can be at most 11 g/l, optionally at most 8 g/l.

Particularly when the separation carried out at the end of the processof the invention comprises filtration using a filter press, thisconcentration is preferably at least 8 g/l, in particular between 10 and15 g/l, for example between 11 and 15 g/l; the subsequent drying step inthe process of the invention is then advantageously carried out byatomisation using a spray diffuser.

The conditions imposed on the silicate concentration in the initial seedpartially determine the characteristics of the silicas obtained.

The initial seed may contain an electrolyte. Nevertheless, it ispreferable that no electrolyte is used during the preparation process ofthe invention; in particular, the initial seed preferably contains noelectrolyte.

The term “electrolyte” has its normal meaning here, ie., it signifiesany ionic or molecular substance which, when in solution, decomposes ordissociates to form ions or charged particles. A salt from the groupformed by alkali metal and alkaline-earth metal salts can be cited as anelectrolyte, in particular the salt of the starting metal silicate andthe acidifying agent, for example sodium sulphate in the case of thereaction of sodium silicate with sulphuric acid.

The second step consists in adding the acidifying agent to the seed withthe composition described above.

Thus, in the second step, the acidifying agent is added to said initialseed until at least 5%, preferably at least 50%, of the quantity of M₂Opresent in said initial seed is neutralised.

Preferably, the acidifying agent is added to said initial seed in saidsecond step until 50% to 99% of the quantity of M₂O present in saidinitial seed is neutralised.

The acidifying agent can be dilute or concentrated; the concentrationcan be between 0.4 and 36N, for example between 0.6 and 1.5N.

In particular, when the acidifying agent is sulphuric acid, itsconcentration is preferably between 40 and 180 g/l, for example between60 and 130 g/l.

When the desired concentration of neutralised M₂O has been reached,simultaneous addition (step (iii)) of the acidifying agent and aquantity of alkali metal M silicate is commenced so that theconsolidation ratio, i.e., the ratio of the quantity of silicate added(expressed as SiO₂)/quantity of silicate present in the initial seed(expressed as SiO₂) is greater than 4 and at most 100.

In one embodiment of the invention, simultaneous addition of theacidifying agent and quantity of alkali metal M silicate is carried outsuch that the consolidation ratio is more particularly between 12 and100, preferably between 12 and 50, most particularly between 13 and 40.

In a further embodiment of the invention, simultaneous addition of theacidifying agent and quantity of alkali metal M silicate is carried outsuch that the consolidation ratio is greater than 4 and less than 12,preferably between 5 and 11.5, more particularly between 7.5 and 11.This embodiment is generally employed when the silicate concentration inthe initial seed is at least 8 g/l, in particular between 10 and 15 g/l,for example between 11 and 15 g/l.

Preferably, the quantity of acidifying agent added during the totalityof step (iii) is such that 80% to 99%, for example 85% to 97% of thequantity of M₂O added is neutralised.

In step (iii), it is possible to carry out the simultaneous additionstep of the acidifying agent and the silicate at a first reaction mediumpH of pH₁, then at a second reaction medium pH of pH₂, such that7<pH₂<pH₁<9.

The acidifying gent used during step (iii) can be diluted orconcentrated: the concentration can be between 0.4 and 36 N, for examplebetween 0.6 and 1.5 N.

In particular, when the acidifying agent is sulphuric acid, itsconcentration is preferably between 40 and 180 g/l, for example between80 and 130 g/l.

In general, the alkali metal M silicate added during step (iii) has aconcentration, expressed as silica, of between 40 and 330 g/l, forexample between 60 and 300 g/l, in particular between 60 and 250 g/l.

The precipitation reaction itself is terminated when the remainingquantity of silicate has been added.

It may be advantageous, particularly following the simultaneous additionstep, to mature the reaction medium over a period of 1 to 60 minutes, inparticular 5 to 30 minutes.

Finally, it is desirable to add a supplemental quantity of acidifyingagent to the reaction medium in a subsequent step followingprecipitation and prior to maturing. This addition step is generallycarried out until the reaction medium reaches a pH of between 3 and 6.5is reached, preferably between 4 and 5.5. It allows all the M₂O addedduring step (iii) to be neutralised and regulates the final pH of thesilica to the desired value for the given application.

The acidifying agent used in this addition step is generally identicalto that used during step (iii) of the process of the invention.

The temperature of the reaction medium is normally between 60° C. and98° C.

Preferably, during step (ii) the acidifying agent is added at atemperature of between 60° C. and 96° C. to the initial seed.

In a further embodiment of the invention, the reaction is carried out ata constant temperature between 70° C. and 90° C. (particularly when theconsolidation ratio is greater than 4 and less than 12) or between 75°C. and 96° C. (particularly when the consolidation ratio is between 12and 100).

In a still further embodiment of the invention, the temperature at theend of the reaction is higher than the temperature at the beginning ofthe reaction: thus, the starting temperature is preferably maintainedbetween 70° C. and 90° C. (particularly when the consolidation ratio isgreater than 4 and less than 12) or between 70° C. and 96° C.(particularly when the consolidation ratio is between 12 and 100), thenthe temperature is increased over several minutes during the course ofthe reaction, preferably to between 75° C. and 98° C., for examplebetween 80° C. and 90° C. (particularly when the consolidation ratio isgreater than 4 or less than 12) or between 80° C. and 98° C.(particularly when the consolidation ratio is between 12 and 100), andkept at this value until the reaction is finished.

A silica slurry is produced after the operations just described. This isthen separated (liquid-solid separation). Separation generally consistsof filtration followed by washing if required. If filtration can becarried out using any convenient method (for example using a filterpress, band filter or rotary vacuum filter), it is advantageouslycarried out using a filter press when the silicate concentration in theinitial seed is at least 8 g/l (and less than 20 g/l), in particularbetween 10 and 15 g/l, for example between 11 and 15 g/l.

The recovered suspension of precipitated silica (filtration cake) isthen dried.

Drying can be carried out using any known means.

Drying is preferably effected by atomisation.

Any suitable atomiser can be used, in particular centrifugal driers,spray diffusers, pressurised liquid sprays or double fluid sprays.

Drying is advantageously effected by atomisation using a spray diffuserwhen the silicate concentration in the initial seed is at least 8 g/l(and less than 20 g/l), in particular between 10 and 15 g/l, for examplebetween 11 and 15 g/l.

The precipitated silica which can be obtained under these conditions ofsilicate concentration using a filter press and a spray diffuser isnormally in the form of substantially spherical spherules, preferablywith an average size of at least 80 μm.

In a still further embodiment of the process of the invention, thesuspension to be dried has a dry matter content of more than 15% byweight, preferably greater than 17% by weight, for example greater than20% by weight. Drying is preferably carried out using a spray diffuser.

The precipitated silica which can be obtained using this embodiment isnormally in the form of substantially spherical spherules, preferablywith an average size of at least 80 μm.

This dry matter content can be produced by direct filtration using asuitable filter (in particular a filter press) to give a filter cakewith the correct content. An alternative method consists in adding drymaterial, for example powdered silica, to the cake in a final step ofthe process, following filtration, to produce the required content.

It should be noted that it is well known that the cake obtained isgenerally not in an atomisable condition principally because theviscosity is too high.

The cake is then disintegrated using known techniques. This operationcan be carried out by passing the cake through a colloidal or ball mill.In addition, the viscosity of the suspension to be atomised can bereduced by adding aluminium, in particular in the form of sodiumaluminate, during the process, as described in French patent applicationFR-A-2 536 380, whose subject matter is hereby incorporated. Theaddition can in particular be made at the disintegration stage.

A milling step can follow the drying step, particularly when therecovered product has been obtained by drying a suspension with a drymatter content of more than 15% by weight. The precipitated silica whichcan then be obtained is generally in the form of a powder, preferablywith an average size of at least 15 μm, in particular between 15 and 60μm, for example between 20 and 45 μm.

Once they have been milled to the desired granulometry, the products canbe separated from any products which do not conform to the average, forexample using vibrating sieves of suitable mesh size, and the nonconforming products which are recovered can be returned to the millingstep.

In a further embodiment of the process of the invention, the suspensionto be dried has a dry matter content of less than 15% by weight. Dryingis generally carried out in a centrifugal drier. The precipitated silicawhich can then be obtained is generally in the form of a powder,preferably with an average size of at least 15 μm, in particular between30 and 150 μm, for example between 45 and 120 μm.

Disintegration can also be carried out.

Finally, the dried product (particularly from a suspension with a drymatter content of less than 15% by weight) or milled product can besubmitted to an agglomeration step in a still further embodiment of theprocess of the invention.

The term “agglomeration” means any process which binds together finelydivided objects to form larger, mechanically resistant objects.

Particular processes are direct compression, wet granulation (ie., usinga binder such as water, silica slurry, . . . ), extrusion and,preferably, dry compaction.

When using the latter technique, it can be of advantage to deaerate(also known as predensification or degassing) the powdered productsbefore compaction to eliminate the air included in the products andensure more regular compaction.

The precipitated silica which can be obtained from this embodiment ofthe invention is advantageously in the form of granules, preferably withdimensions of at least 1 mm, in particular between 1 and 10 mm.

Following the agglomeration step, the products can be calibrated to thedesired size, for example by sieving, then packaged for future use.

One advantage of the powders and spherules of precipitated silicaobtained using the process of the invention is that they can simply,efficiently and economically be formed into granules as described,particularly using conventional forming operations, such as granulationor compaction, and these operations do not cause deterioration which canmask or even destroy the excellent intrinsic reinforcing properties ofthese powders, as could be the case when using the conventional powdersof the prior art.

The invention also relates to novel precipitated silicas having a gooddispersion (and deagglomeration) ability and improved reinforcingproperties, said silicas preferably being relatively large in size andgenerally being obtained using one of the embodiments of the process ofthe invention described above.

In the following description, the BET specific surface area wasdetermined using the BRUNAUER-EMMET-TELLER method described in “TheJournal of the American Chemical Society”, Vol.60. page 809, February1938, corresponding to standard NFT 45007 (November 1987).

The CTAB specific surface area is the external surface area determinedin accordance with standard NFT 45007 (November 1987) (5.12).

The DOP oil absorption value was determined in accordance with standardNFT 30-022 (March 1953) using dioctylphthalate.

The loose packing density (LPD) was measured in accordance with standardNFT-030100.

Finally, the pore volumes given were measured by mercury porosimetry.The pore diameters were calculated using the WASHBURN relation with anangle of contact theta of 130° and a surface tension gamma of 484dynes/cm (MICROMERITICS 9300 porosimeter).

The dispersibility and deagglomeration ability of the silicas of theinvention was quantified using a specific deagglomeration test.

The deagglomeration test was carried out as follows:

agglomerate cohesion was measured by granulometric measurement (using adiffraction laser), carried out on a silica suspension which had beendeagglomerated using ultrasound; the deagglomeration ability of thesilica (breakdown of objects from 0.1 to several dozen microns) was thusmeasured. Ultrasound deagglomeration was effected using a VIBRACELLBIOBLOCK (600 W) sonificator equipped with a 19 mm diameter probe.Granulometric measurements were carried out using a diffraction laser ona SYMPATEC granulometer.

2 grams of silica were measured into a small beaker (height: 6 cm anddiameter: 4 cm) and brought up to 50 grams by addition of deionisedwater: an aqueous suspension containing 4% of silica was thus formedwhich was homogenized for 2 minutes using a magnetic stirrer. Ultrasounddeagglomeration was then carried out as follows: the probe was immersedto a depth of 4 cm and the output power was regulated to produce a 20%needle deviation on the power dial (corresponding to an energydissipation of 120 watt/cm² at the probe tip). Deagglomeration wascarried out for 420 seconds. Granulometric measurement was then carriedout after introducing a known volume (in ml) of the homogenisedsuspension into the granulometer cell.

The medial diameter ø₅₀ obtained was lower the greater thedeagglomeration ability of the silica. The ratio (10× volume ofsuspension introduced in ml)/optical density of the suspension measuredby granulometry, where the optical density is of the order of 20, wasalso measured. This ratio indicated the fines content, ie., the ratio ofparticles of less than 0.1 μm which are not detected by thegranulometer. This ratio, termed the ultrasound deagglomeration factor(F_(D)) is higher when the silica has a higher deagglomeration ability.

A first embodiment of the invention provides a novel precipitated silicacharacterised in that it has the following properties:

a CTAB specific surface area (S_(CTAB)) of between 140 and 240 m²/g,preferably between 140 and 225 m²/g, for example between 150 and 225m²/g, in particular between 150 and 200 m²/g,

an ultrasound deagglomeration factor (F_(D)) of more than 11 ml, forexample more than 12.5 ml,

a medial diameter (ø₅₀), following ultrasound deagglomeration, of lessthan 2.5 μm, in particular less than 2.4 μm, for example less than 2.0μm.

A second embodiment of the invention provides a novel precipitatedsilica characterised in that it has the following properties:

a CTAB specific surface area (S_(CTAB)) of between 140 and 240 m²/g,preferably between 140 and 225 m²/g, for example between 150 and 225m²/g,

a pore distribution such that the pore volume constituted by pores withdiameters of between 175 and 275 Å represents less than 50% of the porevolume constituted by pores with diameters of less than or equal to 400Å,

an ultrasound deagglomeration factor (F_(D)) of more than 5.5 ml,

a medial diameter (ø₅₀), following ultrasound deagglomeration, of lessthan 5 μm.

One feature of a silica in accordance with the second embodiment of theinvention is its pore volume distribution, in particular the pore volumedistribution constituted by pores with diameters of less than or equalto 400 Å. This latter volume corresponds to the useful pore volume offillers which are used to reinforce elastomers. Porogram analysis showsthat silicas in accordance with the second embodiment of the inventionhave less than 50%, preferably less than 40% of their useful pore volumeconstituted by pores with diameters in the range 175 to 275 Å.

Preferably, silicas in accordance with the second embodiment of theinvention have the following properties:

an ultrasound deagglomeration factor (F_(D)) of more than 11 ml, forexample more than 12.5 ml, and/or

a medial diameter (ø₅₀), following ultrasound deagglomeration, of lessthan 4 μm, for example less than 2.5 μm.

The silicas of the invention generally have a BET specific surface area(S_(BET)) of between 140 and 300 m²/g, in particular between 140 and 280m²/g, for example between 150 and 270 m²/g.

In a further embodiment of the invention, the silicas have aS_(BET)/S_(CTAB) ratio of between 1.0 and 1.2, ie., the silicas have alow microporosity.

In a still further embodiment of the invention, the silicas have aS_(BET)/S_(CTAB) ratio of more than 1.2, for example between 1.21 and1.4, ie., the silicas have a relatively high microporosity.

The silicas of the invention generally have a DOP oil absorption valueof between 150 and 400 ml/100 g, more particularly between 180 and 350ml/100 g, for example between 200 and 310 ml/100 g.

The silicas of the invention can be in the form of a powder,substantially spherical spherules or optionally granules, and areparticularly characterised in that, while of relatively large size, theyhave remarkable deagglomeration ability and dispersibility and highlysatisfactory reinforcing properties. They thus advantageously have asuperior deagglomeration ability and dispersibility and a specificsurface area and size which is identical to or close to those of priorart silicas.

Silica powders in accordance with the invention preferably have anaverage size of at least 15 μm, for example, between 20 and 120 μm orbetween 15 and 60 μm (in particular between 20 and 45 μm) or between 30and 150 μm (in particular between 45 and 120 μm).

The loose packaging density (LPD) of said powders is generally at least0.17, for example between 0.2 and 0.3.

Said powders generally have a total pore volume of at least 2.5 cm³/g,more particularly between 3 and 5 cm³/g.

This produces a very good compromise between use and final mechanicalproperties in the vulcanised state.

Finally, they constitute particularly suitable precursors for thesynthesis of granules as will be described below.

The substantially spherical spherules of the invention preferably havean average size of at least 80 μm.

In certain embodiments of the invention, this average spherule size isat least 100 μm, for example at least 150 μm; it is generally at most300 μm and is preferably between 100 and 270 μm. The average size isdetermined in accordance with standard NF×11507 (December 1970) by drysieving and determination of the diameter corresponding to anaccumulated residue of 50%.

The loose packaging density (LPD) of said spherules is generally atleast 0.17, for example between 0.2 and 0.34.

They generally have a total pore volume of at least 2.5 cm³/g, inparticular between 3 and 6 cm³/g.

As indicated above, a silica in the form of substantially sphericalspherules, which are advantageously solid, homogeneous, of lowpulverulence and with good flow characteristics, has a very gooddeagglomeration ability and dispersibility. It also has excellentreinforcing properties. This form of silica also constitutes a highlysuitable precursor for the synthesis of powders and granules inaccordance with the invention.

The dimensions of the granules of the invention are preferably at least1 mm, in particular between 1 and 10 mm, measured along the axis oftheir largest dimension (length).

Said granules can be in a variety of forms. Examples are spheres,cylinders, parallelepipeds, pellets, platelets or circular section ormultilobed extrudates.

The loose packing density (LPD) of said granules is generally at least0.27, up to 0.37.

They generally have a total pore volume of at least 1 cm³/g, moreparticularly between 1.5 and 2 cm³/g.

The silicas of the invention, in particular in the form of a powder,substantially spherical spherules or granules, are preferably preparedusing a suitable embodiment of the process of the invention describedabove.

Silicas in accordance with the invention or prepared using the processof the invention have particular application in reinforcing natural orsynthetic elastomers, in particular tires.

They provide the elastomers with an excellent compromise between theirdifferent mechanical properties, in particular a significant improvementin rupture or tear resistance and, in general, good abrasion resistance.In addition, these elastomers preferably heat up to a lesser extent.

The following examples illustrate the invention without in any waylimiting its scope.

EXAMPLE 1

662 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.4) with a concentration expressed as silica of 7.1 g/l were introducedinto a stainless steel reactor equipped with a propeller stirrer anddouble envelope heater.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 7.1 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 7.3 l/mn for a period of 3 min 20 s; following addition, theneutralisation ratio in the seed was 85%, ie., 85% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 70 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 7.3 l/min, and

a solution of sodium silicate, with a concentration expressed as silicaof 130 g/l, at a rate of 10.1 l/min.

During this simultaneous addition step, the instantaneous neutralisationratio was 92%, ie., 92% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 19.6.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a rotary vacuum filter to recover a silica cake with a losson ignition of 87% (and thus a dry matter content of 13% by weight).

This cake was then fluidised by simple mechanical action. After thisdisintegration operation, the resulting slurry was atomised using acentrifugal drier. The characteristics of silica P1 in powder form (inaccordance with the invention) were as follows:

CTAB specific surface area 159 m²/g BET specific surface area 195 m²/gpore volume V1 represented by 0.94 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.41 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V144% average particle size 60 μm

The deagglomeration test described above was then carried out on silicaP1.

Following ultrasound deagglomeration, the silica had a medial diameter(ø₅₀) of 1.2 μm and an ultrasound deagglomeration factor (F_(D)) of 12ml.

EXAMPLE 2

662 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.4) with a concentration expressed as silica of 51 g/l were introducedinto a stainless steel reactor equipped with a propeller stirrer anddouble envelope heater.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 5 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 5.1 l/mn for a period of 3 min 20 s; following addition, theneutralisation ratio in the seed was 85%, ie., 85% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 70 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 5.1 l/min, and

a solution of sodium silicate, with a concentration expressed as silicaof 130 g/l, at a rate of 7.1 l/min.

During this simultaneous addition step, the instantaneous neutralisationratio was 92%, ie., 92% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 19.5.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a rotary vacuum filter to recover a silica cake with a losson ignition of 87% (and thus a dry matter content of 13% by weight).

This cake was then fluidised by simple mechanical action. After thisdisintegration operation, the resulting slurry was atomised using acentrifugal drier.

The characteristics of silica P2 in powder form (in accordance with theinvention) were as follows:

CTAB specific surface area 182 m²/g BET specific surface area 225 m²/gpore volume V1 represented by 0.93 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.30 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V132% average particle size 60 μm

The deagglomeration test described above was then carried out on silicaP2.

Following ultrasound deagglomeration, the silica had a medial diameter(ø₅₀) of 2.9 μm and an ultrasound deagglomeration factor (F_(D)) of 14ml.

EXAMPLE 3

The process of Example 2 was followed, except for the simultaneousaddition of sulphuric acid and sodium silicate. Thus:

662 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.4) with a silica concentration of 5 g/l was introduced into astainless steel reactor equipped with a propeller stirrer and doubleenvelope heater.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 5 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 5.1 l/mn for a period of 3 min 20 s; following addition, theneutralisation ratio in the seed was 85%, ie., 85% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 70 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 5.1 l/min, and

a solution of sodium silicate, with a silica concentration expressed asSiO₂ of 230 g/l, at a rate of 4.1 l/min.

During this simultaneous addition step, the instantaneous neutralisationratio was 92%, ie., 92% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 19.9.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a rotary vacuum filter to recover a silica cake with a losson ignition of 87.1% (and thus a dry matter content of 12.9% by weight).

This cake was then fluidised by simple mechanical action. After thisdisintegration operation, the resulting slurry was atomised using acentrifugal drier.

The characteristics of silica P3 in powder form (in accordance with theinvention) were as follows:

CTAB specific surface area 215 m²/g BET specific surface area 221 m²/gpore volume V1 represented by 0.93 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.42 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V145% average particle size 60 μm

The deagglomeration test described above was then carried out on silicaP3.

Following ultrasound deagglomeration, the silica had a medial diameter(ø₅₀) of 1.2 μm and an ultrasound deagglomeration factor (F_(D)) of 20ml.

EXAMPLE 4

662 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.4) with a concentration expressed as silica of 3.85 g/l was introducedinto a stainless steel reactor equipped with a propeller stirrer anddouble envelope heater.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 3.85 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 3.9 l/mn for a period of 3 min 20 s; following addition, theneutralisation ratio in the seed was 85%, ie., 85% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 70 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 3.9 l/min, and

a solution of sodium silicate, with a concentration expressed as silicaof 65 g/l, at a rate of 10.9 l/min.

During this simultaneous addition step, the instantaneous neutralisationratio was 92%, ie., 92% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 19.5.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

A slurry of precipitated silica was thus obtained which was siltered andwashed using a rotary vacuum filter to recover a silica cake with a losson ignition of 87.1% (and thus a dry matter content of 12.9% by weight).

This cake was then fluidised by simple mechanical action. After thisdisintegration operation, the resulting slurry was atomised using acentrifugal drier.

The characteristics of silica P4 in powder form (in accordance with theinvention) were as follows:

CTAB specific surface area 210 m²/g BET specific surface area 244 m²/gpore volume V1 represented by 0.89 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.20 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V122% average particle size 60 μm

The deagglomeration test described above was then carried out on silicaP4.

Following ultrasound deagglomeration, the silica had a medial diameter(ø₅₀) of 4.1 μm and an ultrasound deagglomeration factor (F_(D)) of 13ml.

EXAMPLE 5

662 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.5) with a concentration expressed as silica of 5 g/l were introducedinto a stainless steel reactor equipped with a propeller stirrer anddouble envelope heater.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 5 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 5,2 l/mn for a period of 3 min 8 s; following addition, theneutralisation ratio in the seed was 85%, ie., 85% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 70 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 5.2 l/min, and

a solution of sodium silicate, with a concentration expressed as silicaof 230 g/l, at a rate of 4.1 l/min.

During this simultaneous addition step, the instantaneous neutralisationratio was 95%, ie., 95% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 19.9.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a rotary vacuum filter to recover a silica cake with a losson ignition of 86.4% (and thus a dry matter content of 13.6% by weight).

This cake was then fluidised by simple mechanical action. After thisdisintegration operation, the resulting slurry was atomised using acentrifugal drier.

The characteristics of silica P5 in powder form (in accordance with theinvention) were as follows:

CTAB specific surface area 164 m²/g BET specific surface area 194 m²/gpore volume V1 represented by 1.15 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.70 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V144% average particle size 65 μm

The deagglomeration test described above was then carried out on silicaP5.

Following ultrasound deagglomeration, the silica had a medial diameter(ø₅₀) of 1.2 μm and an ultrasound deagglomeration factor (F_(D)) of 12ml.

EXAMPLE 6

662 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.5) with a concentration expressed as silica of 5 g/l were introducedinto a stainless steel reactor equipped with a propeller stirrer anddouble envelope heater.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 5 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 5.2 l/mn for a period of 3 min 9 s; following addition, theneutralisation ratio in the seed was 85%, ie., 85% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 80 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 5.2 l/min, and

a solution of sodium silicate, with a concentration expressed as silicaof 230 g/l, at a rate of 4.1 l/min.

During this simultaneous addition step, the instantaneous neutralisationratio was 95%, ie., 95% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 22.8.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a rotary vacuum filter to recover a silica cake with a losson ignition of 86.1% (and thus a dry matter content of 13.9% by weight).

This cake was then fluidised by simple mechanical action. After thisdisintegration operation, the resulting slurry was atomised using acentrifugal drier.

The characteristics of silica P6 in powder form (in accordance with theinvention were as follows:

CTAB specific surface area 157 m²/g BET specific surface area 193 m²/gpore volume V1 represented by 0.95 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.42 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V144% average particle size 70 μm

The deagglomeration test described above was then carried out on silicaP6.

Following ultrasound deagglomeration, the silica had a medial diameter(ø₅₀) of 1.3 μm and an ultrasound deagglomeration factor (F_(D)) of 10ml.

EXAMPLE 7

662 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.5) with a concentration expressed as silica of 5 g/l were introducedinto a stainless steel reactor equipped with a propeller stirrer anddouble envelope heater.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 5 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 5.2 l/mn for a period of 3 min 30 s; following addition, theneutralisation ratio in the seed was 95%, ie., 95% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 70 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 5.2 l/min, and

a solution of sodium silicate, with a concentration expressed as silicaof 230 g/l, at a rate of 4.1 l/min.

During this simultaneous addition step, the instantaneous neutralisationratio was 95%, ie., 95% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 19.9.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a rotary vacuum filter to recover a silica cake with a losson ignition of 86.7% (and thus a dry matter content of 13.3% by weight).

This cake was then fluidised by simple mechanical action. After thisdisintegration operation, the resulting slurry was atomised using acentrifugal drier.

The characteristics of silica P7 in powder form (in accordance with theinvention) were as follows:

CTAB specific surface area 168 m²/g BET specific surface area 195 m²/gpore volume V1 represented by 0.94 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.47 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V150% average particle size 65 μm

The deagglomeration test described above was then carried out on silicaP7.

Following ultrasound deagglomeration, the silica had a medial diameter(φ₅₀) of 1.1 μm and an ultrasound deagglomeration factor (F_(D)) of 13ml.

EXAMPLE 8

The following were introduced into a stainless steel reactor equippedwith a propeller stirrer and a double envelope heater:

626 liters of water and

36 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.4) with a concentration expressed as silica of 135 g/l.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 7.3 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofsulphuric acid was then introduced at a concentration of 80 g/l and arate of 5.6 l/mn for a period of 3 min 30 s; following addition, theneutralisation ratio in the seed was 67%, ie., 67% of the quantity ofNa₂O present in the initial seed had been neutralised.

The following were then introduced simultaneously into the reactionmedium over 70 min:

a solution of sulphuric acid with a concentration of 80 g/l, at a rateof 5.6 l/min, and

a solution of sodium silicate, with a concentration expressed as silicaof 135 g/l, at a rate of 8.6 l /min.

During this simultaneous addition step, the instantaneous neutralisationratio was 80%, ie., 80% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 16.7.

Following introduction of all the silicate, sulphuric acid introductionwas continued at the same rate for 10 min. This complementary additionof acid brought the pH of the reaction medium to a value of 4.5.

The reaction medium was then allowed to mature for 10 min (with stirringat 85° C.).

A slurry of precipitated silica was thus obtained which was diluted with540 liters of water then filtered and washed using a rotary vacuumfilter to recover a silica cake with a loss on ignition of 88.0% (andthus a dry matter content of 12.0% by weight).

This cake was then fluidised by mechanical and chemical action (additionof a quantity of sodium aluminate corresponding to a Al/SiO₂ weightratio of 3000 ppm). After this disintegration operation, a pumpable cakewas obtained with a pH of 6.4 which was atomised using a centrifugaldrier.

The characteristics of silica P8 in powder form (in accordance with theinvention) were as follows:

CTAB specific surface area 149 m²/g BET specific surface area 200 m²/gpore volume V1 represented by 0.92 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.50 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V154% average particle size 55 μm

The deagglomeration test described above was then carried out on silicaP8.

Following ultrasound deagglomeration, the silica had a medial diameter(φ₅₀) of 2.3 μm and an ultrasound deagglomeration factor (F_(D)) of 17ml.

EXAMPLE 9

The following were introduced into a stainless steel reactor equippedwith a propeller stirrer and a double envelope heater:

750 liters of water and

26.5 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.5) with a concentration expressed as silica of 235 g/l.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 8 g/l. The temperature of the solution was raised to 85° C. withstirring. The entire reaction was carried out at 85° C. A solution ofdilute sulphuric acid with a density of 1.050 at 20° C. was thenintroduced at a rate of 6.0 l/mn for a period of 5 min 35 s; followingaddition, the neutralisation ratio in the seed was 95%, ie., 95% of thequantity of Na₂O present in the initial seed had been neutralised.

Simultaneous introduction of a sodium silicate solution of the typedescription above at a rate of 4.8 l/min and of dilute sulphuric acidalso of the type described above and at a rate which was regulated so asto maintain a pH of 8.5±0.1 in the reaction medium, was then effectedover 75 min.

During this simultaneous addition step, the instantaneous neutralisationratio was 90%, ie., 90% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 13.5.

Following simultaneous addition, silicate introduction was halted anddilute sulphuric acid introduction was continued at for 14 min to reducethe pH of the reaction medium to a value of 4.0.

Introduction of the acid was then halted and the reaction medium wasstirred for 10 min at a temperature of 85° C.

A slurry of precipitated silica was then obtained which was filtered andwashed using a filter press to recover a silica cake with a loss onignition of 81% (and thus a dry matter content of 19% by weight).

This cake was then fluidised by mechanical and chemical action (additionof a quantity of sodium aluminate corresponding to a Al/SiO₂ weightratio of 2700 ppm). After this disintegration operation, a pumpable cakewas obtained with a pH of 6.7 which was atmoised using a centrifugaldrier.

The characteristics of silica P9 in the form of substantially sphericalspherules (in accordance with the invention) were as follows:

CTAB specific surface area 157 m²/g BET specific surface area 194 m²/gpore volume V1 represented by 0.99 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.64 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V164% average particle size 260 μm

The deagglomeration test described above was then carried out on silicaP9.

Following ultrasound deagglomeration, the silica had a medial diameter(φ₅₀) of 1.7 μm and an ultrasound deagglomeration factor (F_(D)) of 19ml.

EXAMPLE 10

The following were introduced into a stainless steel reactor equippedwith a propeller stirrer and a double envelope heater:

733 liters of water and

46.5 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.5) with a concentration expressed as silica of 235 g/l.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 14 g/l. The temperature of the solution was raised to 80° C. withstirring. The entire reaction was carried out at 80° C. and withstirring. A solution of dilute sulphuric acid with a density of 1.050 at20° C. was then introduced at a rate of 5.4 l/mn for a period of 9 min;following addition, the neutralisation ratio in the seed was 78%, ie.,78% of the quantity of Na₂O present in the initial seed had beenneutralised.

Simultaneous introduction of a sodium silicate solution of the typedescribed above at a rate of 4.3 l/min and of dilute sulphuric acid alsoof the type described above and at a rate which was regulated so as tomaintain a pH:

of 8.5±0.1 for the first 55 minutes, then

of 7.8±0.1 for the final 35 minutes,

in the reaction medium, was then effected over 90 min:

During this simultaneous addition step, the instantaneous neutralisationratio was 94%, ie., 94% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 8.3.

Following simultaneous addition, silicate introduction was halted anddilute sulphuric acid introduction was continued for 6 min to reduce thepH of the reaction medium to a value of 4.2.

Introduction of the acid was then halted and the reaction medium wasstirred for 10 min at a temperature of 80° C.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a filter press to recover a silica cake with a loss onignition of 77% (and thus a dry matter content of 23% by weight).

This cake was then fluidised by mechanical and chemical action (additionof a quantity of sodium aluminate corresponding to a Al/SiO₂ weightratio of 3000 ppm plus addition of sulphuric acid). After thisdisintegration operation, a pumpable cake was obtained with a pH of 6.3which was atomised using a centrifugal drier.

The characteristics of silica P10 in the form of substantially sphericalspherules (in accordance with the invention) were as follows:

CTAB specific surface area 149 m²/g BET specific surface area 177 m²/gpore volume V1 represented by 0.94 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.46 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V149% average particle size 240 μm

The deagglomeration test described above was then carried out on silicaP10.

Following ultrasound deagglomeration, the silica had a medial diameter(φ₅₀) of 1.7 μm and an ultrasound deagglomeration factor (F_(D)) of 12ml.

EXAMPLE 11

The following were introduced into a stainless steel reactor equippedwith a propeller stirrer and a double envelope heater:

747 liters of water and

33.2 liters of a solution of sodium silicate (SiO₂/Na₂O molar ratio of3.5) with a concentration expressed as silica of 235 g/l.

The concentration of silicate expressed as SiO₂ in the initial seed wasthus 10 g/l. The temperature of the solution was raised to 80° C. withstirring. The entire reaction was carried out at 80° C. with stirring. Asolution of dilute sulphuric acid with a density of 1.050 at 20° C. wasthen introduced at a rate of 5.4 l/mn for a period of 7 min 20 s;following addition, the neutralisation ratio in the seed was 89%, ie.,89% of the quantity of Na₂O present in the initial seed had beenneutralised.

Simultaneous introduction of a sodium silicate solution of the typedescribed above at a rate of 4.3 l/min and a dilute sulphuric acid alsoof the type described above and at a rate which was regulated so as tomaintain a pH

of 8.5±0.1 for the first 55 minutes, then

of 7.8±0.1 for the final 25 minutes

in the reaction medium, was then effected over 80 min:

During this simultaneous addition step, the instantaneous neutralisationratio was 90%, ie., 90% of the quantity of Na₂O added (per min) wasneutralised.

The consolidation ratio following simultaneous addition was 10.4.

Following simultaneous addition, silicate introduction was halted anddilute sulphuric acid introduction was continued for 10 min to reducethe pH of the reaction medium to a value of 4.3.

Introduction of the acid was then halted and the reaction medium wasstirred for 10 min at a temperature of 80° C.

A slurry of precipitated silica was thus obtained which was filtered andwashed using a filter press to recover a silica cake with a loss onignition of 78.5% (and thus a dry matter content of 21.5% by weight).

This cake was then fluidised by mechanical and chemical action (additionof a quantity of sodium aluminate corresponding to a Al/SiO₂ weightratio of 3000 ppm plus addition of sulphuric acid). After thisdisintegration operation, a pumpable cake was obtained with a pH of 6.6which was atomised using a centrifugal drier.

The characteristics of silica P11 in the form of substantially sphericalspherules (in accordance with the invention) were as follows:

CTAB specific surface area 172 m²/g BET specific surface area 205 m²/gpore volume V1 represented by 1.00 cm³/g pores with d ≦ 400 Å porevolume V2 represented by 0.57 cm³/g pores 175 Å ≦ d ≦ 275 Å ratio V2/V157% average particle size 270 μm

The deagglomeration test described above was then carried out on silicaP11.

following ultrasound deagglomeration, the silica had a medial diameter(φ₅₀) of 2.3 μm and an ultrasound deagglomeration factor (F_(D)) of 18.9ml.

EXAMPLE 12

For comparison purposes, three silicas with CTAB specific surface areasof between 140 and 240 m²/g, suitable for use as reinforcing fillers forelastomers, were studied. These were:

two commercially available silicas in powder form:

PERKASIL KS 404® (reference PC1 below), sold by AKZO,

ULTRASIL VN3® (reference PC2 below), sold by DEGUSSA,

silica (reference MP1 below) in the form of substantially sphericalspherules, from Example 12 in European patent application EP-A-0 520 862(file no 92401677.7).

The characteristics of these silicas are shown in Table I below. Forcomparison purposes, this Table shows the characteristics of silicas P1to P11 in accordance with the invention.

TABLE 1 PC1 PC2 MP1 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 S_(STAR) (m²/g)145 155 160 159 182 215 210 164 157 168 149 157 149 172 S_(S1) (m²/g)183 170 170 195 225 221 244 194 193 195 200 194 177 205 V1 (cm³/g) 0.760.93 0.90 0.94 0.93 0.93 0.89 1.15 0.95 0.94 0.92 0.99 0.94 1.00 V2(cm³/g) 0.26 0.43 0.55 0.41 0.30 0.42 0.20 0.70 0.42 0.47 0.50 0.64 0.460.57 V2/V1 (%) 34 46 61 44 32 45 20 61 44 50 54 64 49 57 Average size 1217 260 60 60 60 60 65 70 65 55 260 240 270 (μm) Ø₅₀ (μm) 9.45 9.9 4.31.2 2.9 1.2 4.1 1.2 1.3 1.1 2.3 1.7 1.7 2.3 F_(D) (ml) 2.2 2.3 6.5 12 1420 13 12 10 13 17 19 12 13.9

EXAMPLE 13

This Example illustrates the use and behaviour of silicas of theinvention and of the prior art in an industrial rubber formulation.

The following formulation was used (in parts by weight):

Rubber SBR 1712⁽¹⁾ 100 Silica 51 Active ZnO⁽²⁾ 1.81 Stearic acid 0.356PPD⁽³⁾ 1.45 CBS⁽⁴⁾ 1.3 DPG⁽⁵⁾ 1.45 Sulphur⁽⁶⁾ 1.1 Silane X50S⁽⁷⁾ 8.13⁽¹⁾Styrene butadiene copolymer type 1712 ⁽²⁾Rubber quality zinc oxide⁽³⁾N-(1,3-dimethylbutyl)-N′-phenyl p-phenylenediamine ⁽⁴⁾N-cyclohexyl2-benzothiazyl sulphenamide ⁽⁵⁾Diphenyl guanidine ⁽⁶⁾Vulcanising agent⁽⁷⁾Silica/rubber coupling agent (sold by DEGUSSA)

The formulations were prepared as follows:

The following were introduced into a rubber kneader (BANBURY) in theorder shown and at the times and temperatures indicated in brackets:

SBR 1712 (t₀) (55° C.)

X50S and ⅔ of the silica (t₀+1 min) (90° C.)

ZnO, stearic acid, 6PPD and ⅓ of the silica (t₀+2 min) (110° C.)

The kneader was discharged (dumped) when the temperature of the chamberreached 165° C. (ie., at about t₀+5 min). The mixture was introducedinto a mixing mill at 30° C., for rolling. The CBS, DPG and sulphur wereintroduced into the mill. After homogenising with three passes, thefinal mixture was rolled into sheets of 2.5 to 3 mm thickness.

The test results were as follows:

1. Rheological Properties

Measurements were carried out on uncured formulations.

The results are shown in Table II below. The apparatus used to carry outthe measurements is indicated.

TABLE II P5 P6 P7 PC1 PC2 MP1 MOONEY Consistency (1) 100 93 98 123 138112 Min. couple (2) 19.0 18.5 18.7 28.0 32.2 20.5 (1) MOONEY MV 200Eviscosimeter (Mooney Large (1 + 4) measurement) (2) MONSANTO 100S flowmeter

The formulations obtained from the silicas of the invention producedlower values.

This translates as easier use of the mixtures prepared from the silicasof the invention, in particular regarding extrusion and rollingoperations which are frequently carried out during tire manufacture(lower energy outlay for mixing, greater ease of injection duringmixing, reduced expansion in the die during extrusion, less shrinkageduring rolling . . . ).

2. Mechanical Properties

The measurements were carried out on vulcanised formulations.Vulcanisation was carried out by raising the formulations to atemperature of 150° C. for 40 minutes.

The following standards were used:

(i) Tensile tests (modules, rupture resistance) NFT 46-002 or ISO37-1977

(ii) Tear resistance tests DIN 53-507

(iii) Abrasion resistance tests DIN 53-516

The results obtained are shown in Tables III and IV below.

TABLE III P5 P6 P7 PC1 PC2 MP1 100% modulus (MPa) 2.3 1.9 1.7 2.9 3.31.9 300% modulus (MPa) 11.1 10.3 8.5 11.7 12.2 8.3 Reinforcing index⁽¹⁾4.8 5.4 4.9 4.0 3.7 4.4 Rupture resistance (MPa) 26.4 24.5 26.0 21.120.9 24.4 Tear resistance (kN/m) 21.0 22.5 21.0 13.7 14.0 20.0⁽¹⁾corresponds to the ratio: 300% module/100% module

These latter results show an overall improvement in the reinforcingeffect conferred by the silicas of the invention with respect to priorart silicas with an equivalent theoretical reinforcing power.

The silicas of the invention produce reinforcing indices which arehigher than those obtained with prior art silicas, ie., a verysatisfactory compromise between the 100% module and the 300% module; thesilicas of the invention produce fairly low 100% modules, indicatinggood silica dispersion, and relatively high 300% modules, indicating ahigh silica/rubber interaction density; while the P7 silica of theinvention had a lower 300% module, at the same time it had an extremelylow 100% module.

The higher reinforcing power of the silicas of the invention was alsoconfirmed by the higher values obtained for rupture and tear resistance.

TABLE IV P5 P6 P7 PC1 PC2 MP1 Abrasion resistance 66 60 65 83 83 75(mm³)⁽¹⁾ ⁽¹⁾The value measured is the abrasion loss: the lower thevalue, the better the abrasion resistance.

Regarding abrasion resistance, it can be seen that the abrasion loss isreduced by 10% to more than 20% with respect the comparison silicas.This is an important advantage in tire applications.

3. Dynamic Properties

The measurements were carried out on vulcanised formulations.

Vulcanisation was effected by raising the temperature of the formulationto 150° C. for 40 minutes.

The results are shown in Table V below. The apparatus used to carry outthe measurements is indicated.

TABLE V P5 P6 P7 PC1 PC2 MP1 GOODRICH temperature 81 80 80 81 86 85 (°C.)⁽¹⁾ ⁽¹⁾GOODRICH flexometer

The temperature obtained using silicas in accordance with the inventionwas relatively low.

EXAMPLE 14

This Example illustrates the use and behaviour of silicas of theinvention and a prior art silica in an industrial rubber formulation.

The following formulation was used (in parts by weight):

Tufdene 2330 Rubber 75 BR 1220 Rubber⁽¹⁾ 25 Silica 51 Active ZnO⁽²⁾ 1.81Stearic acid 1.1 6PPD⁽³⁾ 1.45 CBS⁽⁴⁾ 1.3 DPG⁽⁵⁾ 1.45 Sulphur⁽⁶⁾ 1.1Silane X50S⁽⁷⁾ 8.13 ⁽¹⁾Butadiene polymer 1220 rubber ⁽²⁾Rubber qualityzinc oxide ⁽³⁾N-(1,3-dimethylbutyl)-N′-phenyl p-phenylenediamine⁽⁴⁾N-cyclohexyl 2-benzothiazyl sulphenamide ⁽⁵⁾Diphenyl guanidine⁽⁶⁾Vulcanising agent ⁽⁷⁾Silica/rubber coupling agent (sold by DEGUSSA)

The formulations were prepared as follows:

The following were introduced into a rubber kneader (BANBURY) in theorder shown and at the times and temperatures indicated in brackets:

Tufdene 2330 and BR 1220 (t₀) (55° C.)

X50S and ⅔ of the silica (t₀+1 min) (90° C.)

ZnO, stearic acid, 6PPD and ⅓ of the silica (t₀+2 min) (110° C.)

The kneader was discharged (dumped) when the temperature of the chamberreached 165° C. (ie., at about t₀+5 min). The mixture was introducedinto a mixing mill at 30° C., for rolling. The CBS, DPG and sulphur wereintroduced into the mill.

After homogenising with three passes, the final mixture was rolled intosheets of 2.5 to 3 mm thickness.

Test results were as follows:

1. Rheological Properties

Measurements were carried out on uncured formulations.

The results are shown in Table VI below. The apparatus used to carry outthe measurements is indicated.

TABLE VI P9 P10 PC2 MOONEY Consistency⁽¹⁾ 115 109 132 Min couple⁽²⁾ 26.124.5 31.1 ⁽¹⁾MOONEY MV 200E viscosimeter (Mooney Large (1 + 4)measurement) ⁽²⁾MONSANTO 100S flow meter

The formulations obtained from the silicas of the invention producedlower values.

This translates as easier use of the mixtures prepared from the silicasof the invention, in particular regarding extrusion and rollingoperations which are frequently carried out during tire manufacture(lower energy outlay for mixing, greater ease of injection duringmixing, reduced expansion in the die during extrusion, less shrinkageduring rolling . . . ).

2. Mechanical Properties

The measurements were carried out on vulcanised formulations.

Vulcanisation was carried out by raising the formulations to atemperature of 150° C. for 40 minutes.

The following standards were used:

(i) Tensile tests (modules, rupture resistance) NFT 46-002 or ISO37-1977 (DIN 53 504)

(ii) Tear resistance tests NFT 46-007

(iii) Abrasion resistance tests DIN 53-516

The results obtained are shown in Tables VII and VIII below.

TABLE VII P9 P10 PC2 100% modulus (MPa) 2.6 2.8 3.1 300% modulus (MPa)11.4 13.1 11.1 Reinforcing index⁽¹⁾ 4.4 4.7 3.6 Rupture resistance (MPa)19.4 19.7 17.1 Tear resistance (kN/m) 37.8 39.7 33.0 ⁽¹⁾corresponds tothe ratio: 300% module/100% module

These latter results show an overall improvement in the reinforcingeffect conferred by the silicas of the invention with respect to priorart silicas with an equivalent theoretical reinforcing power.

The silicas of the invention produce reinforcing indices which arehigher than those obtained with prior art silicas, ie., a verysatisfactory comprise between the 100% module and the 300% module; thesilicas of the invention produce fairly low 100% modules, indicatinggood silica dispersion, and relatively high 300% modules, indicating ahigh silica/rubber interactions density.

The higher reinforcing power of the silicas of the invention was alsoconfirmed by the higher values obtained for rupture and tear resistance.

TABLE VIII P9 P10 PC2 Abrasion resistance 56 59 63 (mm³)⁽¹⁾ ⁽¹⁾The valuemeasured is the abrasion loss: the lower the value, the better theabrasion resistance.

Regarding abrasion resistance, it can be seen that the abrasion loss isreduced by about 10% with respect to the comparison silicas. This is animportant advantage in tire applications.

What is claimed is:
 1. Precipitated silica particulates suited fordisintegration and homogeneous incorporation, dispersion anddistribution within vulcanized elastomeric matrices reinforcedtherewith, said precipitated silica particulates comprising a powderhaving a CTAB specific surface ranging from 140 to 240 m²/g, a mediandiameter factor φ₅₀, after ultrasonic disintegration, less than 5 μm,exhibiting an ultrasonic disintegration factor F_(D) greater than 5.5ml, having a BET specific surface ranging from 140 to 300 m²/g, having amean particle size of at least 15 μm, a loose packing density of atleast 0.17, a total pore volume of at least 2.5 cm³/g, a pore volumedistribution such that the volume of pores having diameters ranging from175 Å to 275 Å is less than 49% of the volumes of pores having diametersless than or equal to 400 Å and a DOP oil uptake ranging from 150 to 400ml/100 g.
 2. The precipitated silica of claim 1, wherein the meanparticle size of the powder is between 15 μm and 60 μm.
 3. Theprecipitated silica of claim 2, wherein the mean particle size of thepowder is between 20 μm and 45 μm.
 4. Precipitated silica particulatessuited for disintegration and homogeneous incorporation, dispersion anddistribution within vulcanized elastomeric matrices reinforcedtherewith, said precipitated silica particulates comprisingsubstantially spherical beads having a CTAB specific surface rangingfrom 140 to 240 m²/g, a median diameter φ₅₀, after ultrasonicdisintegration, less than 5 μm, exhibiting an ultrasonic disintegrationfactor F_(D) greater than 5.5 ml, having a BET specific surface rangingfrom 140 to 300 m²/g, having a mean particle size of at least 80 μm, aloose packing density of at least 0.17, a total pore volume of at least2.5 cm³/g, a pore volume distribution such that the volume of poreshaving diameters ranging from 175 Å to 275 Å is less than 49% of thevolume of pores having diameters less than or equal to 400 Å and a DOPoil uptake ranging from 150 to 400 ml/100 g.
 5. The precipitated silicaof claim 4, wherein the mean particle size of the spherical beads isbetween 100 μm and 300 μm.
 6. The precipitated silica of claim 5,wherein the mean particle size of the spherical beads is between 100 μmand 270 μm.
 7. Precipitated silica particulates suited fordisintegration and homogeneous incorporation, dispersion anddistribution within vulcanized elastomeric matrices reinforcedtherewith, said precipitated silica particulates comprising granulateshaving a CTAB specific surface ranging from 140 to 240 m²/g, a mediandiameter φ₅₀, after ultrasonic disintegration, less than 5 μm,exhibiting an ultrasonic disintegration factor F_(D) greater than 5.5ml, having a BET specific surface ranging from 140 to 300 m²/g, having adimension of at least 1 mm along the longest axis thereof, a total porevolume of at least 1 cm³/g, a pore volume distribution such that thevolume of pores having diameters ranging from 175 Å to 275 Å is lessthan 49% of the volumes of pores having diameters less than or equal to400 Å and a DOP oil uptake ranging from 150 to 400 ml/100 g.
 8. Theprecipitated silica of claim 7, wherein the dimension of the granulatesalong the longest axis thereof is between 1 mm and 10 mm.
 9. Avulcanized elastomeric matrix having a reinforcing filler materialhomogeneously dispersed and distributed therethrough, said reinforcingfiller material comprising finely divided precipitated silicaparticulates and said precipitated silica particulates deriving from apowder having a CTAB specific surface ranging from 140 to 240 m²/g, amedian diameter φ₅₀, after ultrasonic disintegration, less than 5 μm,exhibiting an ultrasonic disintegration factor F_(D) greater than 5.5ml, having a BET specific surface ranging from 140 to 300 m²/g, having amean particle size of at least 15 μm, a loose packing density of atleast 0.17, a total pore volume of at least 2.5 cm³/g, a pore volumedistribution such that the volume of pores having diameters ranging from175 Å to 275 Å is less than 49% of the volumes of pores having diametersless than or equal to 400 Å and a DOP oil uptake ranging from 150 to 400ml/100 g.
 10. A vulcanized elastomeric matrix having a reinforcingfiller material homogeneously dispersed and distributed therethrough,said reinforcing filler material comprising finely divided precipitatedsilica particulates and said precipitated silica particulates derivingfrom substantially spherical beads having a CTAB specific surfaceranging from 140 to 240 m²/g, a median diameter φ₅₀, after ultrasonicdisintegration, less than 5 μm, exhibiting an ultrasonic disintegrationfactor F_(D) greater than 5.5 ml, having a BET specific surface rangingfrom 140 to 300 m²/g, having a mean particle size of at least 80 μm, aloose packing density of at least 0.17, a total pore volume of at least2.5 cm³/g, a pore volume distribution such that the volume of poreshaving diameters ranging from 175 Å to 275 Å is less than 49% of thevolume of pores having diameters less than or equal to 400 Å and a DOPoil uptake ranging from 150 to 400 ml/100 g.
 11. A vulcanizedelastomeric matrix having a reinforcing filler material homogeneouslydispersed and distributed therethrough, said reinforcing filler materialcomprising finely divided precipitated silica particulates and saidprecipitated silica particulates deriving from granulates having a CTABspecific surface ranging from 140 to 240 m²/g, a median diameter φ₅₀,after ultrasonic disintegration, less than 5 μm, exhibiting anultrasonic disintegration factor F_(D) greater than 5.5 ml, having a BETspecific surface ranging from 140 to 300 m²/g, having a dimension of atleast 1 mm along the longest axis thereof, a total pore volume of atleast 1 cm³/g, a pore volume distribution such that the volume of poreshaving diameters ranging from 175 Å to 275 Å is less than 49% of thevolumes of pores having diameters less than or equal to 400 Å and a DOPoil uptake ranging from 150 to 400 ml/100 g.